In a system that includes a plurality of networks, protocols used in the networks may be different from one another. A sensor network system illustrated in FIG. 1 includes a network of a communication device (a sensor node) that is provided with a sensor, and a network having a server that processes data obtained from the sensor. In the example of FIG. 1, a routing protocol for an ad hoc network is used in the sensor network, and an Internet protocol (IP) is used in the network including the server. When the sensor node of FIG. 1 transmits a packet to the server, the sensor node generates a packet destined for a gateway (GW) using the routing protocol for an ad hoc network. A payload of the packet generated by the sensor node includes data destined for the server and information indicating that the final destination is the server. The gateway reads the payload of the received packet, and then recognizes that the final destination is the server in the IP network. Then, the gateway generates a packet having a payload that includes the data destined for the server, and transmits the generated packet to the server using the IP protocol. If the changed packet is transmitted from the gateway, the server receives the data transmitted from the sensor node. In this case, a setting is performed in an application that is included in the sensor node, such that the gateway is designated to be a destination of the data destined for the server. Conversely, when data is transmitted from the server to the sensor node, a setting is also performed in an application of the server, such that, the gateway is designated to be a destination of the data destined for the sensor node. Further, the gateway analyzes data so as to determine whether the destination of the data is a device other than the gateway. Thus, when an application that is to be used in the system of FIG. 1 is developed, different settings are performed in the sensor node, the gateway, and the server, respectively. In the example of FIG. 1, the ad hoc network and the IP network are connected to each other through the gateway, but there may be any number of networks included in a transmission route of a packet.
Therefore, a system has been proposed in which a transmission device includes, in a transmission packet, route information that includes addresses of all nodes through which the transmission packet passes until it arrives at a destination node from a node of the transmission device, and each relay device transfers the transmission packet while identifying a transmission destination using the route information. Further, as a related technology, a wireless communication device has also been proposed that stores, in the form of a history, a destination of a packet that was transmitted in the past, or a transmission source that transmitted relay route information, the destination and the transmission source being included in a network in which a multi-hop communication is performed. When there exists a transmission history with respect to a destination of a packet to be transmitted, using the destination of the packet and the history, the wireless communication device adds, to the packet, information indicating that relay processing is to be performed, so as to perform relay processing using the destination of a packet and the history.
For example, some documents such as Japanese Laid-open Patent Publication No. 2013-157752 and Japanese Laid-open Patent Publication No. 2011-055077 are know.
In a system in which a certain device that will transmit a packet to another device in another network includes, in a packet, an address of a device included in a route to a final destination, and the certain device transmits the packet, if the number of nodes through which the packet passes is larger, an amount of route information is larger. Thus, depending on the length of a route, an amount of data that can be transmitted by one packet is restricted. Further, in a method that uses a transmission history, a transmission history created by transfer processing performed in the same network is used, so the method is not suitable for relay processing performed between networks of different protocols.